the paperwork can be perfect and the vial can still be light. weigh it
#coa-reading 2026-05-13
Wednesday56 messages12 participantstimes are UTC
Highlights from this day
- assay_not_purity — a lab that reports "greater than 98%" rather than a number is telling you they did not integrate carefully, thats just me 09:23
- olive_orders — the related substances table is the interesting part. a row of "not detected" means they did not look hard, ill dig out the number 10:09
- deamidation — update from 16 months ago: started asking every supplier for water content and about half now include it 10:17
- typosquat_tay — sorry to jump in certificate is dated before the lot date, is that just sloppiness 14:32
- tail_factor — does purity by hplc at one wavelength miss things 15:26
not detected means nothing
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a lab that reports "greater than 98%" rather than a number is telling you they did not integrate carefully, thats just me
peak RRT area% note
1 0.42 0.31 solvent front
2 0.88 0.44 related substance
3 1.00 98.72 main
4 1.14 0.53 related substancetfa or acetate, how do i tell from the paperwork
net not gross
i have never seen a research certificate with an endotoxin result on it. not once, ill dig out the number
sloppy not sinister
purity is not assay
peak RRT area% note
1 0.42 0.31 solvent front
2 0.88 0.44 related substance
3 1.00 98.72 main
4 1.14 0.53 related substance🎉4👀1🧊1
for the archive purity is what fraction of the contents is the target. assay is how many mg are actually there. different questions
the certificate from KP is the one i use to teach this because it actually has a populated impurity table
no lot number on this certificate, does that make it worthless
the related substances table is the interesting part. a row of "not detected" means they did not look hard, ill dig out the number
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the honest summary is that a certificate tells you what the supplier says about a lot they chose to test, n of 1 obviously
update from 16 months ago: started asking every supplier for water content and about half now include it
ask for water content
looks re-dated
lot_number_loui have never seen a research certificate with an endotoxin result on it. not once, ill…
whats the minimum a certificate has to have before you take it seriously
weigh the vial
unrelated but the font on this one changes halfway down, am i being paranoid
does anyone actually check the residual solvents section
retention time shifts between runs are normal. relative retention time is the number to compare
does anyone keep a folder of certificates to compare over time
test it yourself
good certificate actually
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is sterility tested as part of a normal purity certificate
mixed fonts and inconsistent kerning in one document is worth a second look
two certificates from the same supplier have an identical chromatogram, is that normal
water content is why an honest 10mg vial assays at 9.1. karl fischer titration, and most certificates omit it
why would a vial be 98.6 pure and still assay under label
net peptide is gross mass minus water minus counterion. that is why 11.4mg of powder can be a correct 10mg vial
quick one a supplier certificate on its own is a starting point, not evidence. that is the whole reason the verification channel exists, your mileage will differ
check the lot
residual solvents matter more than people think for anything that went through a lot of purification steps
no lot no certificate
gross mass on a jewellery scale plus the water content is enough to catch most underfills
is endotoxin ever tested on research material
same chromatogram
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coming back to this should a certificate say which instrument and method they used
an identical chromatogram on two different lots is the single biggest tell there is
thats the counterion
a vial can be 99.4% pure and hold 8.1mg of a 10mg label. both numbers are true and only one of them is the one you care about
slightly off topic but one decimal versus two is usually just house style, not precision
for the archive is area percent the same thing as how many mg are in the vial
is there a standard layout or does every lab do their own
sorry to jump in certificate is dated before the lot date, is that just sloppiness
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thats a tell
quick one i was wrong about this for a year: area percent under-reports nothing, it just answers a different question than assay does, happy to be corrected
thats a real table
14:53tenpence pinned a message
follow up i asked GGPeps for the method and they sent it. that alone put them ahead of most
not evidence on its own
no lot number, no certificate. a document you cannot tie to the vial in your hand is decoration
the certificate from SWB is the one i use to teach this because it actually has a populated impurity table
[edited]net not gross
a certificate should name the method, the instrument, the column and the operator. most name none of those
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does purity by hplc at one wavelength miss things
| Line | Claims | Does not claim |
|---|---|---|
| Purity (area %) | fraction of detected material that is the target | how many mg are in the vial |
| Assay / content | mg of target per vial | that it is sterile |
| Water content | mass fraction that is water | anything about purity |
| Counterion | salt form and its mass share | net peptide unless stated |
| Related substances | what else was seen | what was not looked for |
if you only read one line on a certificate, read the lot number. if you read two, read the assay